I'm Lucy, and I'd be happy to answer your questions today. I'm sorry to hear about your situation.
The law of private nuisance says that a property owner has an obligation NOT to interfere with his neighbor's use and enjoyment of his property. So, if removing the tress is causing runoff across your property, you can require them to fix that problem, regardless of who owns the property in the middle. They're not allowed to improve their own property at your expense. In addition to fixing the problem, if you can show that your property has been damaged or the value has been reduced, they can be required to pay to restore your property or compensate you for the lost value.
The term "gore" doesn't appear anywhere in the NJ state statutes in this context (there is one statute that talks about the Highlands region). The fact that the area where they removed the trees is "of questionable ownership" means that you'd need a judge to look at all the evidence and figure out who owns it. That's going to require pulling property records, to start, and you may need to have a survey done. It's possible that the land in question doesn't belong to either of you (in which case, it likely belongs to the city/county). But, legally, no matter who owns the property, they can't create a situation that increases runoff to your property. They have to pay to fix the private nuisance they caused.
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